JPH0733297B2 - Method for manufacturing porous ceramics - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a porous ceramic, which is suitable for a high temperature catalyst carrier and which can maintain a high specific surface area even at high temperatures.

[Conventional technology]

Traditionally, the catalysts used in chemical processes are usually 60
If it was resistant to a temperature of 0 ° C. or lower, it did not particularly hinder the ordinary chemical process. Therefore, even if a ceramics catalyst is generally used, its heat resistance has not been a problem, but in recent years, a device involving a high temperature thermochemical process, in particular, a catalytic combustor is used in a gas turbine, a boiler, a jet engine, or the like. Due to expectations for applications, demand for reduction of NO _x generation, improvement of combustion efficiency, etc., ceramics that are resistant to high temperature environments of 1000 ° C or higher have come to be used, and therefore heat resistance as a carrier for ceramics. Is being reviewed.

Such ceramics are produced by, for example, appropriately mixing and mixing powders of various metal oxides, molding, and firing to obtain a desired composition and shape. However, in this method, since the starting material powder itself has a low specific surface area, the specific surface area is further reduced by high temperature firing, and a highly efficient catalyst cannot be obtained.

Therefore, in order to produce a ceramics having a higher specific surface area, a method of firing a gel powder formed by mixing and hydrolyzing a metal alkoxide instead of a metal oxide powder as a starting material, for example, an aluminum alkoxide or a barium alkoxide, INTERNATIONAL SYMPOSIUM ON FINE CERAMI
It is described in Hiromichi Arai's document entitled "Development of heat-resistant catalytic material in high temperature catalytic combustion" in CS ARITA '87.

However, in the above-mentioned sol-gel method, since it is generated as a powder, it is necessary to re-form it in order to integrally mold the ceramics, and the specific surface area around 1200 ° C, which is the most commonly used temperature as a combustion catalyst. But at most 50
It was as small as ~ 60m ² / g, and the specific surface area was not large enough. Further, in the case of a simple alumina system, there is a problem that during the phase transition to α-alumina, grain growth occurs and the specific surface area is rapidly reduced.

[Problems to be Solved by the Invention]

Therefore, in order to solve the above problems, the present inventor first modified an aluminum alkoxide with an alkanolamine, a β-keto acid ester, or a β-diketone compound in synthesizing an alumina-based porous gel by the sol-gel method. By hydrolyzing with an appropriate amount of water in the presence of the agent and a retarding element such as silicon or phosphorus, a homogeneous alumina-based gel is formed instead of a powder, and it does not shrink or crack due to supercritical drying. By the method of forming an integrated homogeneous alumina-based porous gel, it has a high specific surface area at high temperature,
A method for producing a bulky and bulky precursor gel of alumina-based porous ceramics, that is, an alumina-based porous gel was proposed.

However, the method proposed above has a problem that it takes about 3 days for gelation, and it takes 1 week to 10 days if the aging time is included, resulting in low ceramic production efficiency.

An object of the present invention is to provide a production method capable of easily and efficiently producing an integrated bulky porous ceramic having a high specific surface area at a high temperature by the sol-gel method.

[Means for Solving the Problems]

The present invention is characterized in that a mixture containing a metal alkoxide is hydrolyzed, and an isocyanate ester is added to the obtained sol or solution in an amount of 0.01 mol to 1 mol per mol of the metal alkoxide, followed by heat treatment. This is a method for producing high quality ceramics, and the above object can be achieved thereby.

The isocyanate used in the present invention is not particularly limited as long as it is an organic compound having an isocyanate group, i.e., -N = C = O group, and known compounds can be used. N = C = O) _n (R is a hydrocarbon having n isocyanate groups). Therefore, the number of moles of the isocyanate ester used in the present invention with respect to the metal alkoxide is -N = C = O.
It means the number of moles of the group.

A preferred example of the isocyanate ester used in the present invention is hexamethylene diisocyanate.

The mixture containing a metal alkoxide to be hydrolyzed in the present invention is a mixture containing at least a metal alkoxide, and in addition to the metal alkoxide, undergoes an addition reaction with an organic solvent and a metal alkoxide, and is hydrolyzed to give the original compound. It includes a reactive organic compound having a function of returning to control a so-called hydrolysis reaction, a metal salt, an organometallic compound other than an alkoxide, and the like.

The mixture containing the metal alkoxide is optionally 1/3 to 1/3 of the number of hydrolyzable reactive groups present in the mixture in the presence of a base catalyst such as ammonia, pyridine, piperidine or piperazine. It is hydrolyzed with 10 times the molar amount of water. In this case, if the amount of water is 1/3 times or less, gelation is difficult, and if it is 10 times or more, particles tend to be formed, and the desired homogeneous gel cannot be produced. Water used for the hydrolysis can be used alone or diluted with an organic solvent such as alcohol.

After the hydrolysis reaction of the above mixture, the addition of the isocyanate ester causes the gelation to proceed very quickly, and usually the gelation is completed within a few minutes to a few tens of minutes.

The isocyanic acid ester may be added directly to the hydrolysis reaction mixture, but after removing the solvent in the mixture before the addition, an organic solvent such as dimethylformamide (DMF) is added to the sol or the solution. As a condition, isocyanate ester is added.

The resulting gel is dried and then calcined. The drying step is not particularly limited, but it is preferably performed under supercritical conditions in order to achieve the object of the present invention. Especially CO ₂
It is preferable to remove the organic solvent in the gel by a mixed system with.

The ceramics obtained in the present invention include Al ₂ O ₃ and Zr.
_{O 2, BaO-Al 2 O} 3, La 2 O 3, -Al 2 O 3, Al 2 O 3 -TiO 2, Al 2 O 3
-SiO ₂ system, Al ₂ O ₃ -SiO ₂ -MgO system (cordierite) Al
₂ O ₃ —ZrO ₂ system and the like can be mentioned.

The metal alkoxide used in the present invention is not particularly limited, but is represented by the general formula M (-OR) _n (M represents an n-valent metal atom, for example, Al, Si, Na, K, Ca, Ti, St, Y,
Ba and the like can be mentioned, and Al, Si, Ti, Zr and the like are preferable. R represents a hydrocarbon group, preferably an alkyl group. ).

Examples of the organic solvent for dissolving the metal alkoxide include alcohols represented by methanol, ethanol, n-propanol, iso-propanol, sec-butanol, etc., aromatic hydrocarbons represented by toluene, benzene, xylene, etc., Tetrahydrofuran, dimethylformamide, carbon tetrachloride and the like are exemplified, but alcohols are preferable from the viewpoint of solubility.

Examples of the reactive organic compound for adjusting the hydrolysis reaction, β-keto acid ester, for example, ethyl acetoacetate,
Examples include β-diketone compounds such as methyl acetoacetate and ethyl malonate, such as acetylacetone, alkanolamines such as monoethanolamine and triisopropanolamine.

These reactive organic compounds are mixed and reacted with the metal alkoxide such that the sum of one or more of them is 0.01 to 1 times the mole of the metal alkoxide, and a reaction product is formed. In this case, when the amount is 0.01 times or less, the amount is too small and the effect is thin, which is not preferable, and when the amount is 1 times or more, the gelation is too fast and the handling is not preferable.

In addition, phosphorus, a silicon compound, such as PO (OR) ₃ (R represents an alkyl group) or a partial hydrolysis thereof, which has a function of delaying the α-transition of ceramics, may be added as a mixture if desired. Reactive compounds, halides (eg SiI ₄ , SiBr ₄ , Si ₂ Cl ₆ ), others (eg Si (CH ₃ COO) ₄ etc.), phosphates (eg H ₃ P)
O ₄ , H ₂ PHO ₃ , HPH ₂ O ₂ etc.), inorganic compounds such as metal salts (eg NaCl, MgBr ₂ , TiCl ₄ etc. halides, NaNO
₃ , nitrate such as K ₂ SO ₄ , Ca (NO ₃ ) ₂ , sulfate, etc., organometallic compounds (for example, CH ₃ COONa, acetate such as (CH ₃ COO) ₂ Ca, etc.,
Oxalates such as (COONa) ₂ and (COOK) ₂ , complexes with chelating compounds such as EDTA and NTA), and in some cases finely reactive metal and oxide fine powders (eg, CaO, TiO ₂ , SiO) ₂ , P
₂ O ₅ , ZrO _2, etc.) and the like.

[Action]

The sol formed by hydrolysis is gelled by condensation of OH groups between sol particles. This usually takes time.
However, by adding an isocyanate ester to this, the OH groups on the surface of the sol particles and the isocyanate ester combine to promote gelation between particles. Further, since gelation is not only due to the bond between the particles, the independence of the particles is stronger than in the case where no isocyanate ester is used, and it is considered that the α-transition due to the firing of the gel can be avoided.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 10 g of [(sec-C ₃ H ₇ O) ₃ Al] was placed in 10 ml of 2-C ₃ H ₇ OH, and 5.283 g of ethyl acetoacetate was added. Thereto, 2-C ₃ H ₇ OH
Dilution water consisting of 20 ml and 2.19 g was added for hydrolysis. Next, after removing the solvent with an evaporator, DMF 40
ml was added and dissolved. To this sol, 0.5 ml of hexamethylene diisocyanate was added and gelled for 5 minutes. This gel is supercritical under carbon dioxide (80 ℃, 160kg / c
The solvent was extracted with carbon dioxide at m ² ) and dried to obtain an airgel.

This was calcined at 1200 ° C. for 5 hours, and as a result of X-ray diffraction, the θ phase alone was found to have a specific surface area of 72 m ² / g.

(Example 2) were placed _{[(sec-C 3 H 7 O} ) 3 Al ] 10g into _{2-C 3 H 7 OH 10ml} , was added ethyl acetoacetate 3.52 g. Thereto, 2-C ₃ H ₇ OH
Dilution water consisting of 20 ml and 2.19 g of water was added for hydrolysis. Next, after removing the solvent with an evaporator, DM
40 ml of F was added and dissolved. Hexamethylene diisocyanate (1 ml) was added to the sol and gelled for a few minutes. This gel is subjected to carbon dioxide under supercritical conditions (80 ℃, 160k
The solvent was extracted with g / cm ² ) and dried to obtain an airgel.

This was calcined at 1200 ° C. for 5 hours, and as a result of X-ray diffraction, the specific surface area was 85 m ² / g only in the γ phase and the θ phase. Also 1400
After baking at 5 ° C. for 5 hours, the result of X-ray diffraction was a θ phase only and a specific surface area of 42 m ² / g.

Comparative Example 10 g of [(sec-C ₃ H ₇ O) ₃ Al] was placed in 10 g of 2-C ₃ H ₇ OH, and 5.28 g of ethyl acetoacetate was added. Thereto, 2-C ₃ H ₇ OH
Dilution water consisting of 20 ml and 2.19 g of water was added for hydrolysis. This sol was kept at 60 ° C. for 7 days for gelation and aging. Next, the supercritical condition of carbon dioxide (80
The solvent was extracted at 160 ° C. and 160 kg / cm ² ) and dried to obtain an airgel.

This was calcined at 1200 ° C. for 5 hours, and as a result of X-ray diffraction, the θ phase alone showed a specific surface area of 15 m ² / g. Also, 1400 ℃, 5
In time the specific surface area was 8 m ² / g.

〔The invention's effect〕

According to the present invention, the use of an isocyanic acid ester can drastically reduce the gelation generation time, so that the production time of ceramics is shortened and the quality of the obtained ceramics is Since it is an integrated porous body having a high specific surface area, it has a great effect on increasing the efficiency of high temperature chemical processes.

Claims (1)

[Claims] 1. A method in which a mixture containing a metal alkoxide is hydrolyzed, and an isocyanate ester is added to the obtained sol or solution in an amount of 0.01 mol to 1 mol times the metal alkoxide, followed by heat treatment. Method for producing porous ceramics.